Wall friction device



Nov. 18, 1969 J. L. MCRAE EI'AL 3,478,572

WALL FRICTION DEVICE Filed July 12, 1968 FIG. .1. 5

c o o W 4 5 56 6 IN VENTORS.

' W uomv L. 449x945, Fl 6, 2, JOSEPH w/szocmq United States Patent 3,478,572 WALL FRICTION DEVICE John L. McRae, 416 Groome Drive, Vicksburg, Miss.

39180, and Joseph P. Wislocki, 2352 W. Wilson Ave.,

Chicago, Ill. 60625 Filed July 12, 1968, Ser. No. 744,356 Int. Cl. G01n 3/56 US. Cl. 73-9 8 Claims ABSTRACT OF THE DISCLOSURE A wall friction device comprising a gyratory testing machine for the compaction of samples of soils or paving materials and provided with a mold, and an upper and lower ram for subjecting a test specimen in the mold to pressure. The apparatus further provides an accessory for attachment to the gyratory testing machine mold including a yoke means and jack means actuated by hydraulic means for applying pressure to the yoke means to cause the yoke means to bear against the mold in which the specimen is disposed and gauge means for registering the force bearing against the mold when the yoke means causes movement of the mold with respect to the specimen carried therein.

The present invention relates generally to a materials testing apparatus or device and more particularly, to a wall friction device that can be used to test the wall friction of a specimen which is compacted in a gyratory testing machine, such as that described in US. Patent 2,972,249.

In the gyratory testing machine described in said US. patent, that machine is used to prepare compacted test specimens of the materials approximating the densities developed in finished products, such as the compaction of samples of soils or paving material and the like.

In accordance with the testing machine described in US. Patent 2,972,249, there is provided a compression compaction machine including opposed plungers fabricated to compress materials within a removable cylindrical mold modified by the inclusion of an oscillant mold chuck about the mold. The mold chuck is mounted for gyratory oscillation or Wobble about a point on the axis of the plungers at the base of the material in the mold and oscillated in a conical fashion about the axis of the plungers to produce kneading stresses in the material within the mold. Oscillation of the mold is caused by the camming action of a pair of transverse opposed power driven roller bearings on a radial flange on the mold chuck; the two roller bearings, spaced at 180, bear on opposite faces of the flange and are driven around the flange course by a powered bearing carriage.

It is an object of the present invention to provide a wall friction test device or apparatus for soil testing of soil samples or paving materials which have been compacted in the type of machine described in said US. patent.

Another object of the present invention is to evaluate the internal shearing resistance of granular materials, plastic materials, or granular-plastic combinations of materials, such as soils, bituminous pavement mixtures, in which the resisting force due to friction between the external surface of the test specimen and the wall of the specimen mold or container is isolated and measured separately.

It is yet another object of the present invention to isolate and measure separately the resisting force due to friction between the external surface of the test specimen and the wall of the specimen mold or container, without the use of heavy lubricants between the specimen and the wall of the container which lubricants Patented Nov. 18, 1969 have only been partially successful because the lubricant extrudes under pressure and therefore loses its effectiveness.

It is yet another object of the present invention to provide a wall friction test apparatus for isolating and measuring separately the resistance force due to friction between the external surface of the test specimen and the wall of the specimen mold or container without the use of a lubricant which varies in thickness and introduces error in the measurement of the specimen dimensions.

Another object of the present invention is to provide an apparatus for accurately measuring the wall friction of the specimen without introducing any errors into the measurement as commonly occurred heretofore.

It is another object of the present invention to provide an apparatus for measuring the wall friction of a specimen that has been compacted by a gyratory test machine wherein the roller carriage means of the gyratory test machine can remain stationary during the test.

It is yet another object of the present invention to provide a compact and simple and economical wall friction testing device for use with a compacted specimen which represents a great simplification and saving of time and effort in the conduct of the test, when compared with tests conducted heretofore.

It is yet another object of the present invention to provide an accessory for testing the wall friction of a compacted specimen which can be utilized with a gyratory testing machine and which can be quickly removed therefrom when not in use, so as not to interfere with the use of the gyratory testing machine.

Various other objects and advantages of the present invention will be readily apparent when considered in connection with the accompanying drawings forming a part thereof, and in which:

FIGURE 1 is a perspective view illustrating the wall friction device of the present invention used in combination with a gyratory testing machine; and

FIGURE 2 is an enlarged detailed view of a portion of the device shown in FIGURE 1, partly in section, illustrating the use of the present invention.

Referring to the drawings, they illustrate a complete compacting machine including a gyratory testing machine as described in Patent 2,972,249, provided with a frame 1 including, in addition to vertical members 2, a table 4, and overhead beam 5. The frame supports a hydraulic jack and fluid pressure system described in said patent, and a mold chuck 8, and mold chuck oscillator, motor and gear train described in said patent. The sample 12 of the soil, mix, or other material to be compacted is confined in the open ended cylindrical mold 13 and receives static comprission directly from the heads of axially aligned vertical plungers 14 and 15. Plunger 14 is stationary and depends rigidly from overhead beam 5 while lower plunger 15 is the moving shaft of a hydraulic jack, not shown. Static pressure for compression is imparted to the sample 12 by plunger 15 as actuated by the fluid pressure system. The foregoing structure forms but one arrangement for imparting static pressure to materials confined within an open ended cylindrical mold.

The present invention contemplates a kneading of the material 12 through a gyratory oscillation of the mold 13 while the material is under compression as described above, which is accomplished by providing the compressing plunger 15 with a beveled head 16 loosely fitted within mold 13 and then oscillating the mold 13 With a conical gyration about the bearing surface 17 of head 16, or more specifically, symmetrically about the point defined by intersection of the axis of plungers 14 and 15 with surface 17. To obtain freedom of movement as described for the mold, stationary plunger 14 is provided with floating head 18 secured in any reasonable manner, as for example, by flexible skirt 19 bearing against the end surface of plunger 14 through freely moving ball bearings 20. As the mold is oscillated in this gyratory fashion without rotation, a constant pressure is maintained on lower plunger 15 by means of the fluid pressure system described in Patent 2,972,249, subjecting the sample 12 to the dual stresses of compression and distortion which together constitute kneading. This kneading, or distortion while under compression, ensures a frictional movement and realignment among the particles of sample 12 accomplishing the ultimate in compaction.

The gyratory oscillations imparted to mold 13 are created in mold chuck 8 which includes cylindrical shank portion 21 and peripheral terminal flange 22. Bore 23 of the shank 21 is scaled to an exterior friction fit over mold 13, the shank 21 being provided with expansion slot and compression bolt, described in Patent 2,972,249, to permit insertion of mold 13 in the bore of the shank and frictional retention therein as a result of tightening the bolt. Chuck 8 is provided with a fluid cooling system including ducts 26 and 27 and is flexibly suspended from upper stationary plunger 14 by orienting springs 28 which permit a relatively large field of movement while under tension toward a position of alignment with the plungers 14 and 15. The actual gyrations are caused by cooperation of the flange 22 with roller bearings 29 and 30 which are supported in bearing mounts 31 and 32, respectively, carried by revolving bearing carriage 33. Bearing 29 is adjustably supported on arm 34 so as to bear against the under rim of flange 22 while bearing 30 is positioned to be thrust against the upper rim of flange 22 by pressure exerted on bearing mount 32 by fluid pressure in a cylinder, not shown, as described in US. Patent 2,972,249. This cylinder is attached to carriage 33 at 180 from arm 34, as described in Patent 2,972,249, and is provided with a gauge necessary to control of the pressure exerted through bearing 30, which pressure controls and is a means of measurement of the distortional influence on the sample 12. In the unbiased state, chuck 8 hangs in alignment with plunger 14 with the lower rim of flange 22 just free of pressure from either roller bearing 29 or 30, so as to permit retraction of mount 32 to the extent that bearing 30 retains contact with, but does not exert pressure on flange 22 of the chuck. Manual adjustment of bearing mount 31 controls the maximum amount of distortion obtainable in any specific application while the pressure exerted on mount 32 determines the degree of distortion and therefore the amount of kneading at any particular time. Rotation of carriage 33, which is journaled on the shaft of plunger 14 for rotation on bearings described in Patent 2,972,249, by activation of a motor and gear train, also described therein, causes each point on flange 22 of chuck 8 to be alternately forced up and down by passage of bearings 29 and 30 in rapid succession.

Loading of the compaction machine is accomplished by placing a mold 13 on a tray, described in Patent 2,972,249, filling the mold with the material to be tested, placing the tray and the mold on a platform, running the mold into the chuck by activation of the jack, securing the mold in the chuck and removing the tray by sliding it from between plunger head 16 and the mold. Operation may then be continued by again activating the jack to provide compressing pressure, activating the pressure cylinder described in Patent 2,972,249 and adjusting bearing mount 31, if necessary to cause distortion, and starting a motor to cause the kneading.

In accordance with the present invention, a wall friction test apparatus is provided for testing the wall friction of the specimen 12, which apparatus is generally designated 50. The apparatus comprises two spaced yoke members 52 between which is disposed a central connecting member 54 having an annular ring 56 therein, through the plunger 15 passes. The yoke members 52 are box shaped and have tops 58 and side walls 60 with an open bottom, as best seen in FIGURE 1, so that hydraulic jacks 64 can be disposed thereunder between the table 4 and the tops 58 as seen in the drawings. The annular ring member 56 is provided with an upper rim which extends above the central connecting portion 54 and bears against the lower end or edge of the mold 13. The hydraulic jacks 64 are provided with plungers 68 which project out of the top of the jacks and are actuated by hydraulic means such as oil supplied through lines 70, so as to cause the jack plungers 68 to act against the tops 58 of the yoke members.

The oil supply lines 70 are connected to a hydraulic pump 72 which can be secured by bolts or other suitable means to the vertical members 2. The hydraulic pump 72 is provided with a pump handle 74 and a registering gauge 76.

In operation, when it is desired to test the wall friction between the specimen 12 that has been compacted by the gyratory test machine and the mold wall 13, the wall friction device is positioned in such a way as shown in the drawings and the hydraulic pump 72 is secured to a vertical member 2. Thereafter, the hydraulic system is actuated so that the jacks 64 and their plungers 68 will act against the under side of the yokes 58. A progressively increasing force is applied to the plungers 68 until the rim 66 of the annular ring 56 causes the mold 13 to move with respect to the specimen 12. The amount of force required to overcome the friction between the specimen 12 and the mold wall 13 is registered by the gauge 76. Thus, in this manner, the wall friction device is able to isolate and measure separately the resisting force due to the friction between the external surface of the test specimen 12 and the wall of the specimen mold 13. At this time, the kneading action has been applied by the gyratory testing machine before the wall friction measurement is taken.

In accordance with the present invention, the gyratory shear and gyratory modulus including correction for wall friction is accomplished by two steps. First, the uncorrected gyratory shear values are measured. This is done after the kneading action is applied as described hereinabove in connection with the gyratory testing machine, and as described in the above-mentioned patent.

After completion of the desired compaction eflort using the selected value of strain (gyratory angle) stop the roller carriage 33 with the upper roller just left of the front center position. Then reduce the vertical pressure to zero and then increase the vertical or normal pressure in selected increments, recording both the vertical pressure and the corresponding upper roller pressure for each increment. The height of the sample 12 is also required, and must be recorded for each increment of vertical pressure. The roller carriage 33 remains stationary during this test.

The mold 13 is then released by removing the front half of the mold chuck. The wall friction apparatus is then placed in position as shown in the drawings and as described hereinabove, and the wall friction measurements are taken.

After the yoke members and the two jacks 64 are placed in position for exerting a force which moves the mold 13 upwardly while vertical pressure is maintained upon the sample contained in the mold, the force required to overcome the wall friction and move the mold 13 is determined by observing the pressure gauge of the jack.

The pressure will increase until the force is sufiicient to move the mold with respect to the sample; the pressure gauge reading will then stabilize to the same value after each thrust of the jack and this is the pressure reading that is sought. Wall friction measurements are made at the same increments of vertical pressure that were used when conducting the test for S The load in pounds measured by this method is equal to twice the value of F that is used in the formula that will now be described.

DERIVATION OF FORMULA FOR GYRATORY SHEAR The formula for shear, S and shear modulus, E is derived as follows:

Formulas for calculation of gyratory stability and gyratory modulus including correction for wall friction The gyratory stability is defined as follows:

2-P-l=S -A-h2-F-a 2(Pl+F-a) In like manner, the gyratory modulus is defined as:

Where:

Introducing constants and clearing:

S 52.8P+2.55F

Thus, the present invention provides a device for measuring the wall friction of a specimen after it has been first compacted so that the uncorrected gyratory shear values are measured with the gyratory testing machine, as described in Patent 2,972,249, and this invention further permits this wall friction device to be an accessory to and to be usable with such a type of gyratory testing machine.

Various changes may be made in relative arrangement, form and location of the several parts without departing from the spirit of the invention.

What is claimed is:

1. In a compaction machine comprising a materialconfining mold having open ends and being symmetrical about a central axis, flexibly suspended support means for carrying said material-confining mold, material compressing means having two elongated aligned plungers movable relative to each other along their common axis and each having a terminal material-containing surface normal to said common axis for subjecting material within the material-confining mold to compressive stress axially of said plungers, said common axis of the plungers and the central axis of the material-confining mold being normally coincident, said terminal material-confining surfaces facing each other and being dimensioned to enter the open ends of said material-confining mold with a minimum of clearance, non-aligned bearing means rotatable about said common axis engaging said support means for said material-confining mold for canting said material-confining mold to positions in which the central axis makes an angle with said common axis upon rotation of said bearing means to subject material within said material-confining mold to distortional stresses in addition to static compressive stress axially of said plungers, the improvement including a wall friction device with yoke means having a central section therebetween, fluid jack means for applying a vertical force against said yoke means and central section, said central section having rim means adapted to bear against said material-confining mold to cause said mold to move with respect to material confined within said mold, and means for registering and measuring the moving force required to move said mold.

2. A wall friction measuring device for attachment to a compacting machine comprising yoke means with a central section therebetween, fluid jack means for applying a vertical force against said yoke means and central section to cause a mold member bearing against a specimen to move and means for measuring the moving force required.

3. The device of claim 2 wherein said yoke means includes two spaced apart box members between which is said central section.

4. The device of claim 3 wherein said central section is a flat member with an annular member in the center thereof having a circular raised rim extending above its fiat portion.

5. The device of claim 4 wherein said box members include a top and two vertical side walls and an open bottom.

References Cited UNITED STATES PATENTS 4/1924 Elverson 739 10/1944 Hohwart 737 5/1948 Dasher 739 XR 2/1961 McRae et al. 7388 10/1968 Hecht et al. 739 XR LOUIS R. PRINCE, Primary Examiner WILLIAM A. HENRY II, Assistant Examiner US. Cl. X.R. 

